TOKYO — North Korea tried but failed to launch an intermediate-range missile Friday, American and South Korean military officials said, dealing the regime an embarrassing blow on the most important day of the year in the North Korean calendar. To mark the 104th anniversary of the birthday of the country’s "eternal president," Kim Il Sung, North Korea launched a missile from its East Coast at about 5:30 a.m. local time. But it deviated from a "normal" trajectory, an official from South Korea's Joint Chiefs of Staff told reporters in Seoul.

“North Korea appears to have tried a missile launch from the East Sea [Sea of Japan] area early morning today, but it is presumed to have failed,” the official said.

But South Korea's military is still on high alert. "We are preparing against the possibility that the North could carry out heavyweight provocations at any time, including the fifth nuclear test," a military official said, according to the Yonhap News Agency. A U.S. defense official said that the U.S. Strategic Command systems had also “detected and tracked” the missile. “We assess that the launch failed,” he said.

Initial analysis suggested that the missile was a Musudan, also known as a BM-25, the kind that South Korean authorities had detected being moved Thursday near Wonsan on North Korea’s east coast.

The Musudan is an intermediate-range ballistic missile capable of traveling 1,500 to 2,500 miles — putting the U.S. territory of Guam within reach — and of carrying a 1.3-ton nuclear warhead, according to the Nuclear Threat Initiative. North Korea has displayed the Musudan at its military parades and is believed to have supplied assembly kits for the missile to Iran, but it had never tested this model of missile before.

Jeffrey Lewis, head of the East Asia program at the James Martin Center for Nonproliferation Studies in California, said that the failure would “reinforce the persistent denial” about North Korea’s capabilities.

“But in fact, they will have learned a lot from this launch. Not as much as they would have learned if it had succeeded, but still something,” Lewis said.

The Musudan uses the same sort of engine as the submarine-launched ballistic missile that North Korea tested last year but which also failed.

“Clearly they have a problem, but maybe next time it will work. It took them a couple of launches to get the Taepodong-2 going,” Lewis said, referring to the ballistic-missile technology that has now put two North Korean satellites into orbit. At the same time, North Korea has been making a series of claims about technological advances, from building solid-fuel rocket engines to miniaturizing nuclear warheads. The regime recently claimed that it could send a ­nuclear-tipped missile to the U.S. mainland.

Although this has not been proved, U.S. military officials and nonproliferation experts say that North Korea is clearly working toward this goal. The Musudan test could be part of this program.

At a hearing of a Senate Armed Services subcommittee this week, Brian McKeon, a senior Pentagon official, said that North Korea’s weapons and missile programs pose a growing threat to the United States and its allies in East Asia. North Korea is “seeking to develop longer-range ballistic missiles capable of delivering nuclear weapons to the United States and continues efforts to bring [a road-mobile intercontinental ballistic missile] to operational capacity,” he said.

Although an untested long-range missile was unlikely to be reliable, North Korea’s successful satellite launches showed it was mastering the technologies that would be needed, McKeon said.

Since Kim Jong Un ordered his military to conduct a fourth nuclear test in January — which North Korea claimed as a hydrogen-bomb explosion, although outside experts are highly skeptical — there has been a steady stream of projectiles emanating from North Korea.

North Korea is banned by U.N. Security Council resolutions from launching ballistic missiles or carrying out nuclear tests, but it continues to do so.

The international community has responded to North Korea’s latest provocations with tough sanctions aimed at cutting off the state’s ability to procure parts and finance its weapons-of-mass-destruction program.

This push coincided with two-month-long drills between the U.S. and South Korean militaries, during which they are practicing their response to the collapse of North Korea. The drills, which conclude at the end of this month, include computer-simulated “decapitation strikes” on the North Korean leadership. Amid this background of heightened tensions, North Korea has been preparing for two key events — the anniversary of Kim Il Sung’s birth and the first congress of the communist Workers’ Party in 36 years.

The country is in the grip of a “70-day campaign” to prepare for the congress, set for early next month for the first time since 1980. Analysts expect Kim Jong Un to use the event to bolster his legitimacy.

Kim, who is 33, is not only incredibly young by standards of Korea, where age is revered, but also did not have the kind of long preparation and introduction his father and predecessor, Kim Jong Il, enjoyed.

Douglas Applegate is a Colonel USMCR (retired). Use of his military rank, job titles, and photographs in uniform does not imply endorsement by the U.S. Marine Corps, the Department of the Navy, or the Department of Defense.